Aerodynamic Design of a Centrifugal Compressor Stage

The customer, a leading manufacturer of high speed rotation apparatus and combustion chambers, asked ADT to carry out the complete aerodynamic redesign of a centrifugal compressor stage using TURBOdesign Suite’s inverse design approach.

Performance targets, in terms of pressure ratios and efficiencies, and operating points were set by the customer before the start of the project. Additional requirements on off-design and mechanical performance were also set.

The initial meridional shapes and main dimensions for the compressor stage were produced by means of 1D sizing software, TURBOdesign Pre. The blade loading distribution was optimized using 3D blade design software, TURBOdesign1. This loading distribution was chosen in order to achieve the target pressure ratio at the design mass flow and obtain good compressor impeller efficiency.

Fig. 1. Impeller exit Mach number contours of original (above) and redesigned (below) compressor

The improvements of the stage performance did not exclusively come from the impeller efficiency improvement, but also from the improvement in the uniformity of the flow leaving the impeller. The better blockage factor distribution at the outlet of the impeller for the redesigned blade created a more uniform flow entering the vaneless diffuser downstream of the rotor, improving its performance.

All the designs produced were tested by means of commercial CFD codes. The final design was analyzed for off-design performance, considering different compressor speed lines between 40% and 120% of the design rotational speed.

CFD analysis showed that the final design reached the target pressure ratio, exceeding the stage target efficiency (including the volute) by 2%. Finite Elements Analysis (FEA) was also carried out on the final design, showing an acceptable stress level in the optimized blade considering the material chosen by the customer for the blade manufacturing.